In silver halide color photographic materials, images are formed by reaction of oxidized silver halide developing agent and a dye precursor known as a coupler. In forming such images, it has become relatively common practice in the art to incorporate image-modifying compounds into either the developing solutions or the photographic materials themselves. These image-modifying compounds can impact such photographic properties as sharpness, granularity, contrast and color reproduction.
Incorporation of image-modifying compounds into developing solutions typically limits the ability of the compounds to adequately impact the photographic element since they must diffuse through multiple emulsion, filter or support layers. Direct incorporation of image-modifying compounds into photographic materials, by contrast, often leads to unacceptable image reproduction as such compounds can prematurely interact with other components of the photographic elements, or can decompose during shelf keeping.
It has thus become accepted to attach these image-modifying compounds to coupler moieties and to have them released in an imagewise manner during development of the photographic material. This, however, has the dual disadvantage of requiring image formation (as the coupler moiety reacts with oxidized developer) whenever the presence of an image-modifying compound is desired, and of providing only an imagewise release of the image-modifying compound.
There has recently become known alternative means for incorporating image-modifying compounds into photographic materials. Image-modifying compounds have been inactivated by timing groups which generally release after exposure to hydroxide ions, by blocking groups which release after reaction with some other compound, or by combinations of the two. Specific examples of such image-modifying compounds and their inactivating groups are described in, for example, U.S. Pat. Nos. 4,248,962; 4,409,323; 4,684,604; 5,034,311; 5,283,162; European Patent Application 0 167 168; and in U.S. Pat. No. 5,354,650.
Because timing groups release the compounds to which they are attached after exposure to hydroxide ions, they may, when used alone, prematurely release in the typical water-containing photographic emulsion. Such premature release would allow the image-modifying compounds to diffuse away from their initial location, and would make control over the location where the image-modifying compound acts impractical. For this reason, timed image-modifying compounds are often undesired.
Prior known blocked image-modifying compounds are also often undesired. However, the reason for this is that their release rates--the rate at which they unblock to expose an active image-modifying compound to the photographic material--and/or shelf-life stability are typically pH dependent. That is, known blocking groups have been practically viable only with highly alkaline (pH&gt;13) activator solutions. This has been incompatible with modern commercial processing, especially in the color reversal areas, and thus has made the use of such compounds fairly impractical.
It has further been found that known blocked image-modifying compounds, such as those disclosed in U.S. Pat. No. 5,116,717, can wander within the photographic materials during prolonged shelf-keeping. This can lead to the complete washing out of the image-modifying compound during development, or to the unblocking of the image-modifying compounds at sites other than those intended, thus deleteriously impacting photographic properties.
The blocked image-modifying compounds of U.S. Pat. No. 5,354,650, though ballasted, are provided in an imagewise manner, and after reaction with a second compound that is photographically inert in the layer in which it is coated, or in the form in which it is released. Thus, when it desired to provide image-modifying compounds to photographic materials in a non-imagewise manner, the teachings of U.S. Pat. No. 5,354,650, are inadequate. Further, as the compounds of this reference fail to provide sufficient water solubility, release of active image-modifying compounds in the presence of nucleophiles normally present in processing baths (e.g., sulfite) will be limited, the result being ineffective or improper image modification.